Best Software Design Document Templates

Are you interested in good software design document templates?

What parts of the process take significant amounts of time when you undertake a software development project?

Activities such as gathering the requirements, planning the project, and designing the specifications are good examples. The good news is that you can utilize templates to help speed up these activities and write software documentation efficiently.

In this article, we talk about using software design document templates. If you are an entrepreneur or a software development project manager in an enterprise, these software design document templates will help you.

We start by briefly talking about software design documents. We then move on to the best practices to create such design documents. Finally, we finish by providing a template for a software specification document.

A brief introduction to a software design document

Among the most important deliverables in a software development project is the software design document. Your project’s success depends on getting this right. Just to be crystal clear – Your project will encounter huge problems, even if you have great developers if you don’t get this right.

A software design document (SDD) spells out what your development team will code. It provides a detailed description of the technical solution behind your project. Irrespective of the development methodology used, you need to create an SDD early in the software development lifecycle (SDLC).      

Your work to create an SDD starts when you have the software business requirements document. This document contains the functional requirements and the non-functional requirements (NFRs).

The software architect in your project creates an SDD. This task requires close collaboration with the following roles:

• Business analysts (BAs);
• The lead programmer;
• The test team lead;
• The DevOps team lead.

Architects need to collaborate with infrastructure, cloud architects, and information security specialists too.

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The contents of a design document for a software development project

What should you write in a software design specification? You need to provide the following information:

• Introduction;
• A table of contents;
• An overview of the proposed software system;
• A reference to the software requirements document;
• A summary of the requirements;
• Considerations and parameters you use while designing the solution;
• Assumptions, dependencies, and constraints;
• A reference to the development methodology you are adopting, e.g., Agile;
• Architectural decisions;
• The system architecture pattern you chose;
• An architectural diagram of the proposed software product or application system;
• The development guidelines and practices that you plan to adopt;
• The details concerning the system design, e.g., definitions, classifications, subsystems, interfaces, constraints, external interfaces, processes, etc.;
• Details covering the transaction validation rules;
• Descriptions of the data design and data structures;
• The description of the proposed user interface including wireframes if applicable;
• Description of any API that you need to develop;
• A conclusion;
• A glossary.

Remember that you are addressing the needs of a wide range of stakeholders when you create an SDD. Developers, software designers, testers, DevOps engineers, reviewers, and project managers (PM) will all use this document frequently.

You need to create as detailed an SDD as you can. Use effective tools like Microsoft Word, Excel, Visio, etc. to communicate key information.

A few key considerations while creating a system design document 

Other than the considerations above, when creating a software design document you also need to keep the following key considerations in mind:

• Audience: Developers and testers are the key end-users of an SDD. DevOps engineers and the PM will use it too. When the architect creates an SDD, he/she should think from the perspective of these stakeholders.
• The creator of an SDD: Ideally, we recommend that the software architect creates the SDD. The architect has the required knowledge to make architectural decisions. He/she remains the best person to create the overall technical solution. Having said that, high-visibility projects need professionally-written SDDs. Software quality auditors, regulatory auditors, and many other stakeholders might read such SDDs. You might need professional technical writers to support the architect.
• Review: A detailed design document like SDD needs a thorough review. You need to arrange for an experienced reviewer. Finding such reviewers can take time, therefore, plan ahead.
• Change management: Once you have the SDD reviewed and approved, you need to distribute it to all stakeholders. All relevant stakeholders should only use the latest copy of it. Any change to the SDD must undergo the change management process in your organization.

An example of a helpful software design document template

We will now take you through a useful SDD template. Bradford D. Appleton, the well-known enterprise Agile and DevOps coach has created this helpful SDD template. Several universities utilize this software design template as a part of their software development-related courses.

During this review, we talk about how you create an SDD using this template. The SDD template created by Appleton has the following sections and subsections:

1. Introduction to the SDD including the system overview

You need to provide a general introduction to your project. Talk about the organizational objectives, however, don’t repeat the content of the requirements document.

We don’t recommend you repeat the use cases and user stories in the SDD. Refer to the requirements document but only provide a brief summary of it here.

Talk about the target audience of your SDD. Explain the version-control and distribution mechanisms.

2. Software design considerations including metrics and the user interface design

In this section and associated subsections, you need to explain the specific considerations you factored in while creating the SDD. Touch upon the following aspects:

• Assumptions and dependencies: Describe the assumptions you made about the user interface design and the general system characteristics. Talk about how you validated these assumptions. Elaborate on the external and internal dependencies. If you target specific operating systems like Windows, Mac, Android, or iOS, clarify that.
• Constraints: Talk about the constraints that you had to consider while designing. These could include security, scalability, availability, performance, regulatory standards, etc. Finally, talk about the relevant metrics here such as uptime requirements.
• Goals and guidelines: You need to describe the relevant priorities, principles, goals, and guidelines for designing the proposed application. These could overlap with non-functional requirements (NFRs) like availability. Explain why these principles and goals are key to the proposed system.
• Approaches and methods: Software design is an evolving field, and new approaches/methods emerge. Explain the design methodology and approach you have used.  

3. Decisions that you had to make while choosing the system architecture pattern

This section covers the very first set of decisions that you will make after you receive the software functional description. Architectural decisions influence the architectural pattern you choose. You make these decisions to address not only the functional requirements but NFRs too.

E.g., your architectural decisions influence the following:

• Scalability;
• Maintainability;
• Availability;
• Reliability;
• Testability.

Take a software system with multiple services, for example. Can you separate these services from each other completely? Do they have different peaks and troughs in their demand profile? If you answer affirmatively to these questions, then you can consider the microservices architecture.

4. Details concerning the chosen system architecture pattern

You have explained the project’s architectural decisions in the preceding section. Now, you need to choose an architecture pattern. This is a very important step when you create a technical solution, therefore, you need to get this right.

Large application systems might have several subsystems. You need to explain the architecture patterns for those too.

Remember that this section of the SDD carries plenty of importance. Not just the software development team, but testers and DevOps engineers study this section closely. You need to make this section as clear as you can. Schematic diagrams can help.

We recommend you include relevant architectural diagrams, and these should cover the external interfaces.

There are several popular architecture patterns, e.g.:

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• Layered architecture;
• Event-driven architecture;
• Microkernel architecture;
• Microservices architecture;
• Space-based architecture.

Explain your decisions on why you choose a particular architecture pattern. For strategic software development projects, external software quality auditors might review the SDD. They look for the rationale behind architectural decisions. A well-documented SDD will help you in such cases.

5. Explanations for the design-related choices

While some software development projects can be straightforward, other projects involve complexities. You will face several choices. You need to contend with trade-offs. Design-related decisions and choices are often functions of these trade-offs.

You need to explain your choices and trade-offs. These could involve one or more of the following:

• Infrastructure-related choices, e.g., whether to use a cloud computing platform;
• The kind of cloud computing delivery model to use, e.g., public, private, or hybrid cloud;
• The choice of the technology stack, e.g., MEAN stack (MongoDB-Express.js-Angular.js-Node.js);
• The choice of libraries like jQuery;
• Coding standards and guidelines;
• The choice of application security model;
• The choice of testing frameworks and tools to use;
• The granularity of your requirements traceability matrix;
• The plans for establishing an effective “Continuous Integration” (CI)/”Continuous Delivery” (CD) pipeline;
• Planning the testing and deployment of the application;
• The choice of DevOps tools;
• The choice of external APIs if applicable;
• Planning the maintenance of the software.

You might have many more choices and trade-offs, and the above list is an example only.

6. Detailed system design

In this section, you cover the details at a program or module level. The development team and testers pay plenty of attention to this section, especially software developers who consider this section very important.

Accordingly, you need to provide sufficient details here for everyone who needs them. Avoid jargon and acronyms. Talk about the following aspects:

• The design of each component and module;
• Relevant details of each file;
• How the proposed system delivers its stated functionality;
• The dependencies between different programs;
• Inputs to each program and their outputs;
• The business logic and validation rules for each functionality;
• The resources used by each component or module;
• The tasks performed by each component and the associated user interactions;
• Constraints and assumptions at a subsystem level.

If you have several subsystems that make up the proposed system, then you need to provide a detailed design for each subsystem.

Aspects of a software design document where you need to provide plenty of details

By now, you can see that a software design document requires a lot of details. A few aspects require special attention though.

A software development project always requires a lot of close collaboration, therefore, team members will always share a few details informally. That’s both normal and desirable.

However, this informal approach will simply not work in all cases so you need to provide details upfront. Without that, you can’t consider an SDD complete.

We now talk about these aspects, which are as follows:

1. Capabilities involving cutting-edge technologies

You might choose to offer advanced capabilities in your application, which requires cutting-edge technologies. E.g., you might use Artificial Intelligence (AI) or Machine Learning (ML).

In addition to the standard details in an SDD, you need to explain the technical solutions around these technologies in great detail. E.g., you might need to develop ML algorithms to meet your requirements. Talk about them in detail.

Cutting-edge technologies like ML and blockchain require you to hire a software engineer with niche skills. Naturally, you will want the best value from their effort. An SDD with sufficient details will help developers to become productive far more quickly.

2. Application Security

Security is a key non-functional requirement (NFR), therefore, you might have already talked about it in your SDD. It’s a vast area though. You need to provide sufficient details about your application security solutions.

Talk about the following:

• Whether you would use multi-factor authentication (MFA);
• How you would mitigate the key application security risks;
• Whether you would encrypt data at rest and in transit;
• Whether you would use digital signatures;
• How you would use technologies like firewalls and antivirus;
• Whether you would use cybersecurity threat intelligence capabilities;
• How do you plan to secure APIs?

3. Data models and database design

When you create an SDD, you need to talk about the data models and database design in detail. You need to work closely with the database administrator (DBA) in your organization.

Your development team, testers, and DBA will use the information concerning data models and database design. Cover the following aspects:

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• Entity-Relationship (ER) diagrams for the relational database tables that you will use;
• The database schema for NoSQL databases that you plan to use;
• Performance optimization considerations for programmers and DBAs;
• Database backup and recovery considerations.

4. Your approach to cloud computing

You might use a cloud computing platform in your project. There are different kinds of cloud platforms, which are as follows:

• “Infrastructure-as-a-Service” (IaaS);
• “Platform-as-a-Service” (PaaS);
• “Mobile-Backend-as-a-Service” (MBaaS).

Your project requirements will determine which type of cloud platform you will use. Explain your choice and decision-making process in the SDD.

You might also need to choose a cloud computing delivery model. The various models are as follows:

• Public cloud: You share the cloud infrastructure with other organizations/users. While this delivers cost advantages, you might need to contend with security risks.
• Private cloud: You use a private cloud if you don’t want a shared cloud infrastructure. You exercise full control. However, this model costs more.
• Hybrid cloud: Hybrid cloud is a mix of public and private cloud computing delivery models. While some of your workloads require high security, others might not need it. Workloads that require high security can run on a private cloud. The other workloads can run on a public cloud.

Your decision-making process will depend on your project requirements, information security considerations, and regulatory requirements. Explain your choice and the decision-making process in your SDD.

5. API development

You might use APIs in various ways in your proposed system. In some cases, you might choose to use an external API. It might make sense if you find a well-established provider. Remember that you will add an external dependency for every external API that you use. This could adversely impact the performance of your system, therefore, think through this carefully.

You will likely create your APIs to reflect your core business capabilities. Describe your API development plans in the SDD. Talk about how you would secure the API, furthermore, plan the API endpoint carefully. Formulate the rules for API requests and responses.

Ready to Get Started with Software Design Document Templates?

In this article, we have covered software design documents or technical specification documents. We discussed their importance and what should go into them. Subsequently, we reviewed some key considerations while creating an SDD.

We reviewed a useful software design documentation template. Finally, we highlighted the aspects where you need to provide sufficient details. 

If you, as a business CEO or CTO, require help with software product design and development, DevTeam.Space can help you via its field-expert software developers community.

Write to us your initial project specifications and one of our account managers will get back to you for further assistance.

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